Before and after security analysis of common space implementation (2023)

The concept of common space proposes the integration of road users in order to regulate traffic and improve safety. The main hypothesis is that by promoting smooth traffic and minimizing traffic regulation, people are more alert to other road users, move more slowly, and rely on interactive, deliberation-based actions to decide who has the right of way (Clarke, 2006, Hamilton-Baillie , 2008; Karndacharuk et al., 2014a; Pascucci et al., 2015; Rinke et al., 2017). Because shared spaces depend on interaction to function effectively, this challenges established street separation systems designed to avoid conflicts and limit contact between different road users (Hamilton-Baillie, 2008, Karndacharuk et al., 2014a).

Therefore, shared spaces can be considered low-speed road environments that minimize segregation among road users. In addition to reducing vehicle speeds and providing more space for pedestrians, the aim is to reduce the dominance of motor vehicles and improve the sense of place to further balance the function of the street and make it a public space. (Hamilton-Baillie, 2008, Karndacharuk et al., 2014a).

Despite its goal of improving the safety of vulnerable road users (VRUs), few papers have examined the safety benefits of shared space implementation through before-and-after analysis. Ruiz-Apilánez et al. (2017) highlighted the lack of before and after studies of shared spaces, and this is also documented in the literature review in section 2.1. In particular, several existing before-and-after analyzes of shared spaces have focused on studying changes in the spatial behavior of road users. Safety of vulnerable road users. Some studies include analyzes of traffic conflicts that are more relevant to road safety; however, the considered conflict-based approaches have some drawbacks: 1) In many cases, conflicts are identified in a qualitative way, which increases the subjective element and increases 2) they limit the analysis and often lead to the comparison of conflict rates in before and after scenarios without taking into account the more complex relationship that exists between conflicts and accidents.

This study proposes a conflict-based approach to assess road safety before and after the implementation of shared spaces, filling a gap in the literature that lacks procedures to explicitly identify and quantify the safety benefits of these urban solutions. In particular, the method presented here addresses the two main problems mentioned above: 1) detection and identification of collisions using quantitative methods, using an alternative safety measure called Time to Avoid Collision Points (TTAC); 2) applying extreme value theory (EVT) ) approach was used to model the probabilistic relationship between conflicts and accidents.

The procedure is structured with practicality in mind; therefore, it aims to be a theoretically sound method that should also be relatively easy to apply by practitioners.

A real-world case study is used to illustrate the application of the proposed method. It should be seen as a training ground for a better understanding of the advantages and limitations of the method, and not as an end in itself. In this sense, the analysis of case studies is a good way to show the main features of the program, but also to draw relevant conclusions and suggest practical rules due to some of its limitations.

The remainder of the paper is structured as follows: Section 2 presents a prior literature review on before-and-after shared space analysis, safe alternatives for vehicle-VRU crashes, and methods for extracting crash probabilities from crash data; Section 3 provides an overview of the methods used; Chapter 4 presents the case study and data collection and preparation procedures; Chapter 5 illustrates the results of the before and after analyses; Chapter 6 discusses the main findings; outlook.